$ C = \left[\begin{array}{rrr}1 & 0 & 0 \\ 1 & 2 & 1 \\ 0 & 0 & 1\end{array}\right]$ What is $ C^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}1 & 0 & 0 \\ -\frac{1}{2} & \frac{1}{2} & -\frac{1}{2} \\ 0 & 0 & 1\end{array}\right]$